1. Field of the Invention
This document relates to a liquid crystal display and a driving method thereof.
2. Discussion of the Related Art
Flat panel displays include a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting display (OLED), etc.
Since the LCD satisfies the trend toward lightweight, thin, short and small electric appliances and has improved mass productivity, cathode ray tubes have been rapidly replaced with LCDs in many applications. An active matrix type LCD which drives liquid crystal cells using thin film transistors (hereinafter, referred to as “TFTs”) has been rapidly developed to realize an increase in size and a high resolution by a recent mass production technology and the results of research and development and has been quickly replacing cathode ray tubes in many applications.
A liquid crystal display is driven in an inversion method for inverting the polarities of data voltages charged in a liquid crystal display panel in a predetermined pattern in order to prevent degradation of liquid crystal. However, a data voltage charged in the liquid crystal display panel is biased toward one polarity or another according to the correlation between an image pattern input to the liquid crystal display and a polarity pattern of the liquid crystal display panel, and a common voltage shift is generated due to the biased polarity, thereby degrading display quality.
A pattern of an input image that degrades the display quality in the liquid crystal display may be defined as a problem pattern (or weak pattern), and problem pattern images include an image having white data and black data alternating in subpixels, an image having white data and black data alternating in pixels, a crosstalk check pattern containing a white display surface in a black background, and so on. In addition, the problem pattern includes interlace data in which odd-numbered line data and even-numbered line data are separated.
The present applicant proposed a method for compensating for a biased polarity of a data voltage or a common voltage shift by changing polarity control signals for controlling the polarity of a data voltage charged in a liquid crystal display panel upon input of an image of a problem pattern in Korean Patent Application 10-2007-0052679 (2007-05-30), Korean Patent Application 10-2008-0055419 (2008-06-12), and Korean Patent Application 10-2008-0032638 (2008-04-08). As a result of applying the previously filed applications to a liquid crystal display, degradation of display quality in an image of a problem pattern can be prevented. However, if a pixel array structure of the liquid crystal display panel is changed, the problem pattern image that degrades the display quality of the liquid crystal display panel is also changed. When the problem pattern image is changed due to a change in the pixel array structure, the polarity pattern of the liquid crystal display panel therefore should be changed.
Accordingly, there is a demand for a method which is capable of adaptively changing a problem pattern image, which is defined differently according to a model of a liquid crystal display, and a polarity pattern of a liquid crystal display panel for preventing degradation of the display quality in the problem pattern image. Furthermore, an algorithm and circuit for implementing an adaptive polarity pattern controlling method has to be implemented in a manner that requires no large-capacity memory.